The following invention relates to pattern discrimination test system for early glaucoma detection, and more particularly to a video system which displays to a subject a movable coherent dot pattern within a background of randomly changing dots.
Psychophysical testing in primary open angle glaucoma has three primary functions: (1) to characterize any loss of visual function which has occurred; (2) to provide a basis for predicting the future course of the untreated disease; and (3) to monitor the effects of treatment.
Psychophysical evaluation of the visual field has long been the method used for the clinical diagnosis of glaucoma. Presently, such evaluation is largely limited to the measurement of increment thresholds for small circular achromatic stimuli (e.g., conventional kinetic and static perimetry). The earliest signs of glaucoma found by such tests may include: vertical enlargement of a blind spot; small 37 wedge-shaped" scotomas in the area surrounding the macula; small nasal steps (sensitivity differences between the upper and lower nasal field); increased variability of sensitivity at some visual field locations. These defects may later expand to become "Bjerrum scotomas," which arc from the blind spot around the macula to the horizontal nasal meridian. Bjerrum scotomas often appear simultaneously in the upper and lower field, but the upper and lower defects are rarely, if ever, symmetrical. The fovea is usually spared until late in the disease, and patients with a nearly total loss of visual field may retain essentially normal foveal sensitivity and acuity.
It has been shown recently that conventional kinetic and static visual fields testing do not provide a full indication of loss of optic nerve fibers which is the generally agreed-upon cause of loss of visual function.
The loss of optic nerve fibers can be seen indirectly in abnormal cupping of the optic disk and directly in histologic studies of glaucomatous eyes. Fiber loss can also be observed directly in the retinal nerve fiber layer by photographing the fundus in red-free light.
Using a variety of techniques, prior art investigators have now convincingly shown that the visual field can sometimes appear normal even after substantial fiber loss. Field defects revealed by conventional perimetry may thus be a much less sensitive indicator of glaucomatous nerve damage than was previously suspected.
The pattern of fiber loss in glaucoma is not yet completely understood. Complicating factors include the fact that strict retinotopic correspondence is not maintained in a single fiber bundle. Therefore, a strictly focal pattern of fiber loss does not imply a corresponding pattern of sharply defined, localized scotomas.